Laser range finders (herein abbreviated LRF) are devices that can determine the range from an LRF device to a target without having to physically measure the distance between the two. LRF devices thus provide a quick means, on the order of nanoseconds, for determining the distance between a system, equipped with an LRF device, and a target. Knowing the distance between a system and a target, quickly, can aid tanks and fighter planes in destroying enemy targets by providing distance to target measurements that accurately determine the type of weapon to use on a target and its angle of launch.
Known in the art of laser range detection is the method of time-of-flight measuring. This method is commonly used in LRF devices for determining the distance between a system, equipped with an LRF device, and a target. The time-of-flight measuring method works as follows. A system, equipped with an LRF device, emits laser radiation towards a target. Some of the radiation impinging upon the target will be reflected back towards the system. The time it takes for the emitted laser radiation to impinge upon the target and reflect back towards the system is measured. The speed at which the emitted laser radiation propagated towards the target and reflected back to the system is known, since laser radiation is a form of electromagnetic radiation, and all electromagnetic radiation essentially travels at the speed of light. With knowledge of the speed of propagation of the emitted laser radiation, and the amount of time the emitted laser radiation traveled from the system to the target and back to the system, the distance between the system and the target can be determined, as is known in the art.
It is noted that the time-of-flight measuring method requires a system, utilizing the method, to provide a laser pulse towards a target and to receive reflections of the laser pulse from the target. Systems utilizing the time-of-flight method are therefore susceptible to being detected by laser detector systems.
LRF systems and methods using the time-of-flight measuring method are common in the art. U.S. Pat. No. 5,870,180 issued to Wangler, and entitled “Time measurement device and method useful in a laser range camera” is directed to a device and a method for determining the range at which a target is located. The device includes a light transmitter for transmitting light during a time interval to be measured, and a light receiver for receiving the transmitted light. The light transmitter includes a light emitting diode, to which an electrical current is provided, for generating a constant output light source for the light transmitter. The light transmitter is also responsive to start and stop signals. The light receiver includes charged coupled devices (CCD), each having a linear response to an amount of exposure to light received from the light transmitter.
The range at which a target is located is determined by transmitting light, using the light transmitter, towards a target. Light is transmitted for a time period between the start and stop signals. Light transmitted towards a target is reflected back from the target to the receiver. The receiver receives the reflected light from the target, and provides an output signal, related to an amount of exposure to the reflected light during the time period between the start and stop signals, to the transmitter. The output signal thus provides a measurement of the time period between the start and the stop signals. The time period can be used to determine the range at which the target is located at.
U.S. Pat. No. 6,023,322 issued to Bamberger, and entitled “Laser range finder with target quality display and scan mode” is directed to a device for determining the range at which a target is located. The device includes a laser transmitting section, a laser receiving section and a microcontroller. The device also includes a circular in-sight field of view which incorporates within it a magnified “TV view” of the target area. Above and below the TV view are indicators which include a target quality indicator, a target range display and a sensitivity mode indicator. Within the TV view is an aiming reticle which roughly indicates the footprint of the laser pulses emitted by the device for range finding, such that a target can reliably be selected.
The device emits a series of laser pulses from its laser transmitting section. The device times the flight time of each pulse from the device to a target and back to its receiving section. An average flight time for the pulse series is calculated to determine the range to the target. The microcontroller uses a pulse stack and a comparator to detect and identify valid pulse returns and the number of pulse returns. By aiming the device at various targets using the reticle, a user can move the device around the target to find a surface proximate to the target with a reflective quality sufficient to yield an accurate reading.
U.S. Pat. No. 5,969,676 issued to Tran et al., and entitled “Radio frequency interferometer and laser rangefinder/designator base targeting system” is directed to an apparatus for passively detecting and locating sources of radio frequency (RF) signals from a moving vehicle and for determining the range from the moving vehicle to the RF sources. The apparatus works as follows. RF emissions from an RF source are received by two linear radio frequency interferometer (RFI) arrays located on a common geometric plane on a moving vehicle. Each RFI array produces a signal, indicative of the angle of arrival of the RF signals emitting from the source, with respect to its particular array. The signals from the RFI arrays are used to generate an output signal representative of the position, in terms of latitude, longitude and horizontal range, to the RF source. With the two linear RFI arrays, a line-of-sight vector can be determined, and other systems, such as a digital terrain elevation database (DTED) or a laser rangefinder/designator (LARD), can be provided with this information in order to provide further details of the position of the RF source.
The LARD determines the range to the RF source by directing a laser beam at the RF source. Reflected beams from the RF source are received by the LARD and analyzed by it. The result of the analysis is used to determine a precise range to the RF source. The range calculated by the LARD can be used to further correlate the RF source location with the line-of-sight vector determined by the two linear RFI arrays, and by other systems, such as a DTED.